Intermediates for emetine



United States Patent 3,282,944 INTERMEDIATES FOR EMETINE Thomas Walker, Wembley, England, Rupert Frederick Keith Meredith, Rhondda, Glamorgan, Wales, and Alexander Crawford Ritchie, Harrow, England, assignors to Glaxo Laboratories Limited, Greenford, Middlesex, England, a British company N0 Drawing. Original application May 23, 1961, Ser. No. 111,908, now Patent No. 3,105,835, dated Oct. 1, 1963. Divided and this application July 6, 1962, Ser. No. 213,080

Claims priority, application Great Britain, May 27, 1960,

18,899/ 60 3 Claims. (Cl. 260-287) This application is a division of Serial No. 111,908, now issued on October 1, 1963, as Patent No. 3,105,835.

This invention concerns novel intermediates for use in the chemical synthesis of emetine and its analogues, and to processes for the prepaTation of such analogues.

The alkaloid emetine is widely used, particularly in Asia and Africa, to combat amoebic dysentery. A number of synthetic substances have been suggested as substitutes for this naturally occurring compound but none has been found to be more satisfiactory in practice. In consequence there exists a demand for a synthetic process leading to emetine which is capable of producing the alkaloid more cheaply than by the present extraction from the natural source. Several synthetic processes have, in fact, been proposed but so far as we are aware, none has proved satisfiactory for commercial purposes,

In copencling US. patent application Serial No. 40,200, we have described compounds and processes for use, inter alia, in the synthesis of emetine and its analogues, one of which processes comprising the reaction of a compound having the skeletal structure I (where groups R represent hydrogen atoms or organic groups which may be the same of diflerent) with a substance able to introduce onto the N-atoms a side chain which can condense with the central carbonyl group to form the fi-membered C ring present in emetine. Two such side chains were exemplified, namely and COCH R (where R and R are organic groups). The resulting compound having two identical side chains is then subjected to ring closure, whereupon one only of the chains condenses with the central carbonyl group while the other remains unreacted to protect the N-atom to which it is attached in later stages of the synthesis.

3,282,944 Patented Nov. 1, 1966- We have now found that a compound having the skeletal structure (where R represents an inert group as hereinafter defined and R has the above meaning) is in some respects even more convenient as an intermediate in the synthesis of emetine than is the symmetrical compound of structure I above. Where emetine itself is required the group R should be removable without afiecting the remainder of the molecule and for this purpose an arylmethyl group, preferably .a benzyl group is especially suitable.

If, however, the desired final product is an N-substituted emetine analogue, the group R maybe conveniently either the desired N-substituent or a group which can be converted thereto. Such groupings include alkyl, :alkenyl and aralkyl groups, which may if desired carry substit-uents inert in the various reactions to be outlined below.

The compound II, in order to synthesise emetine or one of its analogues, may then be substituted at the secondary amino group with a side chain which is able to condense with the central carbonyl group, in particular a group CI-I CH COR where R represents an organic group, for example an alkyl, aryl, aralkyl group etc.

. The group CH CH COR rnay conveniently be int-rotion of a carbonyl group with a reactive hydrogen atom.

Where the side chain is -CH CH COR the cyclisation is preferably carried out in the presence of a basic catalyst. The cyclised product is an alcohol of the general formula (III) (where R, R and R have the above meanings). The product is then dehydrated, preferably after isolation. Cyclisation conditions which can be used include, for example alkali metal hydroxides in a water-miscible polar solvent e.g. a lower alcohol, tetrahydrofu-ran, dioxan etc; sodium hydride or sodamide suspended in a suitable solvent e.g. benzene, toluene etc.; but the preferred method is an alkali metal alkoxide in the appropriate alcohol ad- III (1) (where R, R and R have the above given meanings) although some material may be formed in which the unsaturation in the O-ring is differently placed.

Where compounds of skeletal Formula III(1) are to be converted into emetine or its analogues, the C-ring unsaturation may be reduced e.g. by reduction with a metal/ amine or, preferably, a metal/ammonia reducing system. The metal is advantageously an alkali metal or alkaline earth metal, e.g. sodium, potassium, calcium etc. lithium being, however, preferred. The compound to be reduced may be added to the ammonia or amine solution of the metal in an inert solvent e.g. an ether such as diethyl ether ortetrahydrofuran or a hydrocarbon solvent such as benzene or toluene.

Such reduction generally leads to compounds in which the hydrogen atom introduced at the 2-position is in the arather than the fi-configurat-ion. We have found that the a-i'somer can be converted into the fi-isomer, for example by equilibration under strong enolising conditions, e.g. in the presence of concentrated aqueous acid or organic or inorganic base. The .acid may, for example, be a mineral acid such as hydrochloric, sulphuric or phosphoric acid while theibase may be, for example, an alkali metal hydroxide such as sodium or potassium hydroxide, or a tertiary nitrogen base such as triethylamine.

We have also found that it is the B-isomer which leads to emetine and its analogues and it is necessary to effect the conversion described above where these compounds are required. Where conditions in any subsequent reac tions-steps are strong eneolising conditions, however, the separate step of conversion may not be required.

Where compounds are required in which the 3-position side chain is alkyl rather than acyl, the carbonyl group of the acyl group may be reduced, e.g. by reaction with hydrazine and alkali (Wolff-Kishner reaction) or by the action of a metal/acid reducing system (Clemmensen reduction) An alternative method is to convert the carbonyl group into a thioketal group, for example by reaction with ethane di-thiol, and to reduce. this for example with Raney nickel or Raney iron, cobalt etc. or with hydrazine and alkali. It should be noted that Wolff- Kishner reaction conditions are often vigorous enough to hydrolyse vmethoxyl or other ether groups which may be present in the aromatic rings. Such groups may be restored, however, by reaction with appropriate etherifying agents.

Compound H also of use in an alternative route by which emetine may be obtained. In this method group CO.CH R is attached at the NH group of compound II, e.g. by reaction with an anhydride or acid halide, the resulting side chain then being cyclised, preferably in the presence of a basic catalyst, for example potassium tertiary butoxide. In this case, however, the predominant product is a compound of the formula III (2) will remain substantially inert in the cyclisation and dehydration and the term inert substituent is used in that sense herein. The nature of R is preferably also such,

that it remains unaflected in such further steps as Wolff- Kishner reduction and metal/ ammonia reduction. Preferably R should also be removable from the N-atom,

to which it is attached without disruption of the molecule (since the intermediate II will then be of use in the synthesis of emetine or analogues possessing a free NH grouping) except where it is a substituent of a nature:

desired in the final molecule.

The compound II may be substituted in the 3,4,5,6,7 and/ or 8 position of both the isoquinoline rings by a wide variety of groupings and may thus be used to prepare a large number of emetine analogues. The substituents should of course be inert in the attachment of the side chain to the secondary nitrogen atom and the subsequent cyclisation reaction and will be chosen having regard to the nature of the substituent or substituents present in the alkaloid or other compound it is desired to synthesise. Suitable substituents are thus for example alkyl, aralkyl,

aryl, alkoxy, aralkoxy, aryloxy, or tertiary amino groups;

e.g. methyl, ethyl, propyl, isopropyl, butyl, amyl, benzyl,

pheny1,methoxy, ethoxy, propoxy, butoxy, benzyloxy, phenoxy, or dialkylamino groups. substituents may also occupy more than one position, as in methylene dioxy groups. In order to prepare emetine itself the 6, 7, 6' and 7' positions only of compound II should carry methoxy groups and the symbols R should represent hydrogen atoms. I

Compound II may be prepared in any convenient way. A number of methods are given herein and form the present invention.

part of (l) A compound having the structure may be reacted with an isoquinoline pseudo base having the strucure.

(where R and R have the meanings given above). Preferably the groups R are either all hydrogen atoms or one of the groups R attached to the terminal carbon is a carboxyl group while the other three groups R are hydrogen atoms. In the last-mentioned case, the carboxyl group splits off during the condensation.

Where all the groups R are hydrogen atoms the condensation is advantageously carried out in the presence of an acid or, preferably, a basic catalyst. We prefer to effect the reaction at room temperature in a solvent,

such as an alkanol and one suitable system is ethanol containing anhydrous sodium carbonate. Other bases are suitable, however, for example sodium ethoxide, sodium hydroxide, trimethylamine or piperidine but generally give lower yields.

Where one of the terminal groups R is a carboxyl group, however, the terminal hydrogen atom is activated and the condensation will generally take place in the absence of a catalyst. keto carboxylic acids, the reaction is preferably carried out at room temperature or below. The reaction solvent is preferably a lower alkanol, with or without water present, but other polar solvents such as ketones e.g. acetone, MEK etc. ethers such as tetrahydrofuran, dioxan, etc. substituted amides such as dimethylformamide etc. may also be used in the presence or absence of water. Acid or basic catalysts may be present but are not generally required and may reduce rather than increase the yield.

Compound 1V may be prepared'by reacting a compound of structure compounds of Formula VII are acetone, acetoacetic acid and acetone dicarboxylic acid. Care should be taken that suflicient compound VII is present in the reaction mixture to ensure that a minimal quantity of compound I is formed.

Where all the groups, R of compound IV are to be hydrogen atoms, compound VII is conveniently acetone or acetoacetic acid. This reaction may be carried out with an approximately 1:1 mixture of reactants in a basic solution such as pyridine in the case of acetone or merely in water in the case of acetoacetic acid.

Where one of the terminal groups R of compound IV is a carboxyl group, compound VII is conveniently acetone dicarboxylic acid.

The ratio of reactants is advantageously about 1:1 and In view of the instability of 6-.

ture

(where R has the above meaning and X is an anion) which may then be reacted with alkali, preferably in the cold, to form the pseudo base.

(2) A compound having the structure I HCR:

(where R and R have the meanings given above), may be reacted with compound VI shown above under substantially the same conditions as are described for the reaction of compounds VI and VII above. Preferably symbols R all represent hydrogen atoms or three represent hydrogen atoms while one of the two groups attached to the terminal carbon atom is a carboxyl group.

Compound VIII may be prepared by reacting compound V with compound VII, under such conditions that only one molecule of V condenses with each molecule of VII. The conditions for carrying out the condensation are similar to those described in (1) above.

In all the reactions described above, the compounds represented by the skeletal structures shown may be substituted with the groupings desired in compound II. In particular, when close analogues of emetine are to be the final products, the 6 and 7 postiion of the isoquinoline moities should carry methoxy groups. Most of the compounds having structures II, III, IV, V and VIII are new compounds and such new compounds form part of the present invention.

a When the groups R are all identical, compound II possesses two asymmetric carbon atoms, namely at position 1 and 1 and it therefore exists in the form of two pairs of enantiomorphs. In the synthetic processes described, all four isomers of compound II are formed and since only one of these leads to natural emetine or its analogues in the same stereoisomeric series, resolution is required at some stage in the overall synthesis. We have found that in the case Where the groups R are all hydrogen and R is benzyl, and the 6, 7, 6' and 7' position-s carry methoxy groups the racemates may be separated by solubility differences of the salts. One of the racemates, which we have termed isomer A, can he precipitated as its hydrochloride from methanol with ethanolic hydrogen chloride, while the other, isomer B, remains in solution and may be isolated as a sparingly soluble hydrobromide. Resolution of the separated racemates may be effected :at this stage or later in the synthesis We have shown thatthe present isomer B is in the same stereochernical series as natural emetine.

In order that the invention may be well understood we give the following examples by way of illustration only. All temperatures in C.

7 EXAMPLE ,1

v (a) 2-benzyl-3,4-"dihydr0-6,7-dimeth0xyisoqzlirwlinium bromide 3,4-dihydro-6,7-dimethoxyisoquinoline (9.0 g.) in sodium-dried benzene (70 ml.) was treated with redistilled benzyl bromide (6.0 ml.; 1.05 mol.) whereupon a partly solid gum separated. After 1 hr., the product had solidified to a yellow powder (13.4 g., M.P. 178-82") which separated from ethanol in pale yellow tablets (12.5 g.; 73% M.P. 189-91). Crystallisation from ethanol gave the analytical specimen M.P. 198-200. Found: C, 60.3; H, 5.5; N, 3.8; Br, 21.9%. C H O N Br requires C, 59.7; H, 5.5; N, 3.9; Br, 22.1%.

(b) Z-benzyl-I,Z,3,4-tetmhydm-1-hydr0xy-6,7- dimethoxyisoquinoline (1) A solution of 2-benzyl-3,4-dihydro-6,7-dimethoxyisoquinolim'um bromide (50 g.) in water (1800 ml.) was cooled to 6 and aqueous sodium hydroxide (280 ml., 0.6 N) was added dropwise with stirring over 3 hr. The product was filtered, washed with water and dried in vacuo giving a pale yellow powder (42 g.; 100%) M.P. 107-8". crystallisation from benzene-petroleum ether (40-60") gave the analytical specimen M.P. 111. Found: C, 72.0; H, 7.1; N, 5.0% C H O N requires C, 72.2; H, 7.1; N, 4.7%.

(2) 2-benzyl-3,4-dihydro-6,7-dimethoxyisoquinolinium bromide (15.6 g.) was dissolved in aqueous trimethylamine (25% w./v.) (100 111118.) to give a clear yellow solution. When the solution was scratched and allowed to stand at room temperature a fine white precipitate was obtained. After one hour this was removed by filtration washed well with water and dried in vacuo at room temperature. Wt.=11.58 g. (92%) M.P. 112-115 C. (d).

(c) 6,7-dimethxy-1,2,3,4-tetrahydr0-is0quinol- I-yl-acetoacetic acid 6,7-dimethoxy-3,4-dihydroisoquinoline (24 g.) was dissolved in methanol (48 ml.) and water (192 ml.) The mixture was cooled to below room temperature in cold water, and a solution of acetone dicarboxylic acid 18.5 g.) in water 48 m1.) added. After 2% hr. with continuous cooling and occasional shaking the fine white solid was filtered, washed with Water, industrial methylated spirits and finally with ether. After drying in vacuo at room temperature, the product weighed 19.2 g. M.P. l01-3 (decomp.) (Found: C, 60.92- H, 6.56; N, 4.57. C H 9O N requires C, 61.42; H, 6.53; N, 4.78%.)

(d) 2-benzyl-6,7-dimethoxy-1 (6',7-dimeth0xy-1,2',3,4'- tetrahydro-isoquinol-l-yl-acet0nyl) 1,2,3,4 tetrahydroisoquinoline. Isomers A and B 1) 2 benzyl 1,2,3,4 tetrahydro 1 hydroxy-6,7- dimethoxyisoquinoline (10.8 g.) was dissolved in industrial methylated spirits (54 ml.) at room temperature. 6,7-dimethoxy-1,2,3,4 tetrahydroisoquinol-l-yl-acetoacetic acid (9.2 g.) was added and the mixture allowed to stand with occasional shaking. A slow effervescence occurred and the suspension gradually dissolved. After 1% lit. a little undissolved solid was removed by filtration, and the solution treated with saturated ethanolic hydrogen to pH 1.0 with cooling. After standing overnight in the refrigerator the resultant solid was filtered off, washed with industrial methylated spirits, and dried in vacuo at room temperature to give the hydrochloride of isomer A. Wt.=6.6 g. (30%) M.P. 145-8 (d). (Found: C, 59.80; H, 6.79; N, 3.96; Cl, 10.89 C H O N -2HCl-2H O requires C, 60.09 H, 6.93; N, 4.38; Cl. 11.09%.)

Treatment of the filtrate with ether gave an orange yellow gum, which was separated from solvent by decantation and drying in vacuo. This was dissolved in water (200 ml.) and excess ammonium bromide added portionwise with scratching. The pale yellow percipitate was filteredoff, treated with industrial methylated spirits and 8 allowed to stand in the refrigerator overnigh The product was filtered, washed with the same solvent followed by ether and dried in vacuo to give the hydrobromide of isomer B. Wt.=4.1 g. M.P. 152-5 (d).

(Found: C, 54.91; H, 6.2; N, 4.12; Br. 22.52.

' dissolved in 95% ethanol (9.5 ml.) containing anhydrous sodium carbonate (0.025 g.), and the solution was allowed to stand at room temperature for 12 hours then in the refrigerator for 2 days. Water was then added and the mixture was extracted with benzene. The benzene extract was washed with water, dried (MgSO and evaporated to dryness. The resulting oil (2.29 g.) was dissolved in industrial methylated spirits (25 ml.), and ethanolic hydrogen chloride was added to pH 1. The solution was cooled, and crystals (0.53 g., 18%), M.P. 150 of the hydrochloride of isomer A were deposited. Starting material (0.12 g.) was obtained from the mother liquor.

In other experiments, sodium hydroxide, sodium ethoxide, trimethylamine, or piperidine were the catalysts used. The yields varied from 13 to 26%.

EXAMPLE 2 2 benzyl-l-(6',7-dimeth0xy-2'-(3-keto .but-1-yl)-1',2',3, 4 tetrahydro-isoquinol 1 -acet0nyl )-6,7-dimethoxy-1, 2,3,4;tetrahydro-isoquinoline (A series) The hydrochloride of isomer A prepared in Example 1(b) (3 g.) was dissolved in water and the solution brought to pH 10 with aqueous sodium carbonate solution. The mixture was extracted with benzene (1x20 ml., 2X10 ml.). The first two extracts were combined and washed withwater (3 X30 ml.) the washes being backextracted with the third benzene extract. .The combined benzene layers after drying (MgSO had a volume of 45 mls.

Methyl vinyl ketone (0.825 ml.) was added and the mixture allowed to stand overnight at room temperature in vacuo to give a pale gummy residue. Addition of ether, followed by removal of the solvent in vacuo gave a pale foam which was not characterised further but was used for the next stage. Wt.=2.78 g.

The process was repeated using the hydrochloride of isomer B prepared in Example 1 and the product used without purification in the next stage.

EXAMPLE 3 3 aeetyl-2-hydr0xy-9JO-dimethoxy-Z (2-benzyl-6',7'-dimethoxy-1',2',3,4' tetrahy ro-isoquinol-l'yl-metl1yl) 1,2,3,4,6,7-hexahydr0-11 b [H] -benz0 [a] -quinolizine hydrochloride (A series) The A series product from the preceding example (2.78 g.) was dissolved in benzene mls.) and sodium methoxide (0.29 g.) in methanol (5.5 mls.) added with mechanical stirring at room temperature. After 15 minutes an equal volume of water was added. The layers were separated and the aqueous phase extracted with benzene (2X25 mls.). The first two extracts were combined and washed with water (3X50 mls.) the washes being back extracted with the third benzene extract. The combined dried (MgSO benzene layers were evaporated to dryness in vacuo at room temperature and ether (ca. 50 mls.) added. After ca. 15 mins. a white solid (66 I mg.) separated and wasremoved by filtration.

The mother liquors were evaporated to dryness and Ethanoli-c hydrogen chloride was added, withvigorously and after a few minutes a fine white solid was deposited. The suspension was allowed to stand in the refrigerator overnight when the solid was harvested, washed with industrial methylated spirits and dried at room temperature in vacuo to give the desired hydrochloride. Wt.=1.93 g. (55% from starting hydrochloride) M.P. 198 C. (d). Found: C, 61.24; H, 7.15; N, 3.52; C], 9.55. C H O N Cl -2H O requires C, 60.95; H, 7.10; N, 3.95; Cl, 9.99.

The free base had M.P. 148-9. (Found: C, 71.94; H, 7.25; N, 4.4; C H O N requires C, 71.97; H, 7.38; N, 4.66%.)

The process was repeated with the B series product of Example 3 and the product was isolated at the hydrochloride M.P. 187-9. (Found: C, 62.61; H, 7.39; N, 3.76; Cl, 10.0. C H O N Cl -H O requires C, 62.51; H, 7.0; N, 4.05; Cl, 10.2%.) The free base had M.P. 178-9. (Found: C, 71.93; H, 7.61; N, 4.46; C H O N requires C, 71.97; H, 7.38; N, 4.66%.)

EXAMPLE 4 3 acetyl 9,10-dimethoxy-Z (2'-benzyl-6',7'-dimeth0xy-1',

2,3',4' tetrahydroisoquinol 1 yl-methyl) -1,4,6,7- tetrahydro 11 b [H ]-benz [a] -quin0lizine The A series hydrochloride prepared in Example 3 (1 g.) was dissolved in water and adjusted to pH 10 with aqueous sodium carbonate. The mixture was extracted with benzene (3 x 10 mls.). The first two extracts were combined and washed with Water (3 25 mls.), the washes being back extracted with the third benzene extract. The solvent was removed from the combined, dried (MgSO benzene extract and the residual gum heated on the steam 'bath with 11 N sulphuric acid (20 mls.) under nitrogen for 2 /2 hours. The pale yellow solution was cooled and adjusted with sodium hydroxide to pH 6. and then with aqueous sodium carbonate to pH 10. Before neutralisation had been achieved an orange gum separated which did not dissolve either in excess alkali or in benzene (20 mls.) which was now added. The solvent layers were decanted and the gum dissolved in methanol, diluted with water, and poured into the water/ benzene mixture when it was not re-precipitated. The layers were separated and the aqueous phase extracted with benzene (2X20 mls.). The benzene (2X20 m1s.). The benzene layers were washed with water (3 X25 mls.) in the usual way and dried (MgSO Removal of the benzene in vacuo at room temperature, followed by evaporation of the residue with ether gave a pale pink foam. Addition of ether and scratching gave a pale crystalline solid. This was filtered ofi, washed with ether and dried in vacuo at room temperature to give the desired product. Wt.=0.44 g. (53 g.) M.P. 145-6 C.

Found: C, 73.19;H, 7.20;N, 4.50%. C H O N /2H O requires C, 73.07; H, 7.32; N, 4.74%. I.R. carbonyl stretching frequency 1678 cm.-

The process was repeated using the B series isomer prepared in Example 3 and the product was isolated as the free base M.P. 132-1335. Found: C, 73.96; H. N, C35H4205Ng requires C, 74.19; H, 7.27; N, 4.81%.

EXAMPLES Z-benzyl-3,4-dihydr0-6,7-dimethoxy-zsoquinolinium bromide 3,4-dihydro-6,7-dimethoxyisoquinoline (50 g.) was dissolved in industrial methylated spirits (250 ml.) and benzyl bromide (33.5 ml.) added portionwise with cooling at room temperature. The mixture was seeded and scratched, and after 1 /2 hr., the quaternary bromide was 10 filtered off, washed with a little industrial methylated spirits and dried in vacuo at room temperature.

Wt.=43.7 g. M.P. 192-5 A second crop (9.67 g.) was obtained 'by the addition of petroleum ether (B.P. 60-80") to the mother liquors.

EXAMPLE 6 3 acetyl 1,2,3,4,6,7 hexahydro 9,10 dimethoxy- 2 (2 benzyl 1,2,3,4 tetrahya'ro 6,7 dimethoxyisoquinol 1 yl methyl) 11 b[H ]-benz0 [a]quin0liz- Me A SERIES Calcium metal (1.6 g.) was added to liquid ammonia (300 ml.) and the mixture stirred under reflux for 30 min. The conjgated ketone (A series) obtained in Example 3 (10 g.) in a mixture of benzene (50 ml.) and ether ml.) was added over about 3 .min. to the reaction mixture with vigorous stirring. After 10 mins. excess metal was destroyed by the addition of acetone, and the ammonia removed by evaporation. Water (100 ml.) and benzene .(50 ml.) were added and the mixture filtered through kieselgu-hr. The layers were separated, and the aqueous phase extracted with further portions of beneze (2X50 ml.). The benzene extracts were washed with water, the solvent removed in vacuo, and the residue triturated with ether (30 ml.). The crude solid obtained was dissolved in 11 N-sulphuric acid and heated in the steam bath under nitrogen for 2 hr. After cooling, and basification with potassium carbon-ate, the mixture was extracted with benzene, the extracts being washed with water in the usual way. Distillation of the solvent and crystallisation of the residue from ether gave the desired saturated ketone, M.P. 107-109" C. (Found: C, 73.7; H, 7.8; N, 4.7. C H O N requires C, 73.9; H, 7.6; N, 4.8%). The hydrochloride gave prisms from methanol-ether, M.P. 206-20'8 C. ((1). (Found: C, 62.0; H, 7.3; N,3.9; Cl, 9.7. C 5H O N '2HCl2JH O requires C, 62.3; H, 7.3; N, 4.0; 01. 10.2%.)

B SERIES The conjugated ketone (E series) obtained in Example 3 (2.57 g.) in dry tetrahydrofuran ml.) was added to a stirred solution of lithium (0.315 g.) in liquid ammonia (approx. 400 ml.) and the mixture stirred at the boiling point for 30 min. The excess metal was destroyed by the addition of acetone, and the crude product isolated with benzene as in the previous example. The crude product, after partial purification on a Florisil column, was heated on the steam bath overnight in 2 N-hydrochloric acid to effect equilibration, and the product isolated as before with benzene. crystallisation from ether gave the desired saturated ketone M.P. 142.5-144" C. (Found: C, H, N, 4.4. C35H4405N2'2H2O requires C, 72.8; H, 7.6; N, 4.7%.)

The hydriodide gave pale yellow crystals from water. (Found: C, 49.5; H, 6.1; N, 2.9; I. 28.8.

requires C, 49.3; H, 5.75; N, 3.2; I, 29.0%.)

The perchlorate crystallised from water, M.P. -181 C. (Found: C, 52.25; H, 6.2; Cl, 8.2. C36H44O5N2'2HO104'2H2O requires C, H, Cl, 8.6%.)

EXAMPLE .6

Preparation of thioketals A SERIES The saturated ketone (A series) obtained in Example 5 (0.9 g.) was suspended in anhydrous methanol (18 ml.) and saturated with dry hydrogen chloride at 0 C. Ethane dithiol (0.9 ml.) was added, and the passage of gas continued for a further 2 hr. at 0 C. After standing overnight at room temperature, the methanol was removed by distillation in vacuo, water and benzene added, and the mixture neutralised to pH 10 with aqueous sodium carbonate. The free base was isolated with benzene in the usual way, and then isolated as the hydrochloride by treatment with 2 N-hydrochloric acid. After crystallisation from alcohol, the hydrochloride had M.P. 205208 C. (Found: C, 57.1; H, 7.2; N, 3.3; C1, 8.9; S, 8.2.

C H O N S 2HCl 3 5H O requires C, 57.3; H, 7.2; N, 3.5; Cl, 8.9; S, 8.05%.) Thioketal B SERIES 'I he saturated ketone (B series) obtained in Example 5 was converted into the thioketal by the above procedure. The product was isolated as the hydrobromide from ethanol-ether, M.P. 212 C. (Found: C, 52.35; H, 6.3; N, 3.1; S, BI, 18.0- C3 H4 04N2S2'H Br'6H2O requires C, 52.1; H, 6.4; N, 3.2; S, 7.3; Br. 18.2%.)

EXAMPLE 7 Preparation of N-benzylisoemetine The thioketal (A series) obtained in Example 6 (0.41 g.) in xylene (30 ml.) was refluxed with vigorous stirring with Raney nickel (W4; approx. 6 g.) for 16 hr. The nickel was filtered from the cooled reaction mixture, washed with benzene, and the combined filtrate and washings washed with 2 N-sodium hydroxide and water. Removal of the solvent gave a crude foam whose solution in 2 N-hydrochloric acid, on treatment with excess aqueous potassium iodide solution, gave N-benzylisoemetine hydriodide, M.P. 198202 C.

EXAMPLE 8 Preparation of N-benzylemetine Preparation of isoemetine N-benzylisoernetine obtained in Example 6 (0.5 g.) was dissolved in water (50 ml.) containing ZN-hydrochloric acid (10 ml.) and added to a pre-reduced suspension of 10% palladium-charcoal catalyst (0.6 g.) in water (50 ml.) containing2 N-hydrochloric acid (2.5 ml.). The mixture was shaken with hydrogen at atmospheric pressure and room temperature for 18 hr., when the catalyst was removed by filtration and washed with Water. Basification of the aqueous filtrate with sodium carbonate and extraction with ether gave (i) isoemetine as a pale froth, identical (infrared and paper chromatography) with an authentic sample. The hydrochloride, crystallised from methanol-ether had M.P. 254-6 C. (Found: C, 59.2; H, 8.0: N,'4.4; Cl. 12.2. C H N O -2HCl-2H O requires C, 59.1; H, 8.2; N, 4.75; CI, 12.0%.)

EXAMPLE 10 Preparation of (i) emetine Catalytic hydrogenation of (i) N benzylemetine (0.29 g.) with 10% palladium-charcoal catalyst in dilute hydrochloric acid solution, and isolation of the product as 12 above gave (i) emetine, isolated as the hydrobromide (0.12 g.), M.P. 228232 C. ((1) (Found: C, 50.1; H, 6.9; N, 4.1; Br, 22.3. C H O N -2HBr-3H O requires C, 50.0; H, 6.95; N, 4.0; Br, 22.9%).

The infrared spectrum ('bromoform) and R value of this product were identical with those of the hydrobromide of natural emetine.

We claim:

1. A compound of the formula COR where R is lower alkoxy and R is lower alkyl.

2. A compound of the formula R /\l R N COR 1 i R R where R is lower alkoxy and R is lower. alkyl.

3. A compound of the formula where R is lower alkoxy, R is lower alkyl and X is selected from the group consisting of oxygen and ethylene thioketal.

References, Cited by the Examiner UNITED STATES PATENTS 7/1962 Brossi 260-289 2/1964 Barton et al. 260-288 

1. A COMPOUND OF THE FORMULA 2-(HO-),2-((2-(PHENYL-CH2-),6,7-DI(R-),1,2,3,4TETRAHYDROISOQUINOL-1-YL)-CH2 -),3-(R1-CO-),9,10-DI(R-)1,2,3,4,5,6,7,11B-OCTAHYDROBENZO(A)QUINOLIZINE WHERE R IS LOWER ALKOXY AND R1 IS LOWER ALKYL. 